When a stuffing box is fitted with a lantern ring, be
sure to replace the packing beyond the lantern ring at
the bottom of the stuffing box, and be sure that the
sealing water connection to the lantern ring is not
blanked off by the packing (fig. 6-21). Sleeves fitted at
the packing on the pump shafts must always be tight.
These sleeves are usually made secure by shrinking or
keying them to the shaft. Be careful to ensure the water
does not leak between the shaft and the shaft sleeves.
In some pumps, the shaft sleeve is pressed onto the
shaft tightly by means of a hydraulic press, and the old
sleeve must be machined off in a lathe before a new one
can be installed. On other centrifugal pumps, the shaft
sleeve is a snug slip-on fit, butted up against a shoulder
on the shaft and held securely in place with a nut. On
some small pumps, new sleeves can be installed by
removing the water end casing, impeller, and old shaft
sleeves. New sleeves are carried as repair parts, or they
can be made in the machine shop. On large pumps, the
sleeves are usually pressed on; these pumps must be
disassembled and taken to the machine shop, a repair
ship, or a Navy yard to have the old sleeve machined
off and a new one pressed on.
Some sleeves are packed to prevent water leakage
between the shaft and the sleeve, while some have O rings
between the shaft and the abutting shoulder. For detailed
information, consult the appropriate manufacturers
technical manual or applicable blueprints.
Shaft alignment must be checked frequently.
When the shafts are out of line, the unit must be
realigned to prevent shaft breakage and damage to the
bearings, the pump casing wearing rings, and the throat
bushings. Shaft alignment should be checked with all
piping in place.
A FLEXIBLE COUPLING may connect the
driving unit to the pump. You should remember that
flexible couplings (fig. 6-22) are intended to take care
of only slight misalignment. Misalignment should
never exceed the amount specified by the pump
manufacturer. When there is excessive misalignment,
the coupling parts are punished severely, and pins,
bushings, and bearings have to be frequently replaced.
The driving unit may be connected, or coupled, to
the pump by a FLANGE COUPLING. Frequent
realignment of the shaft may be necessary. Each pump
shaft must be kept in proper alignment with the shaft of
the driving unit. Abnormal temperatures, abnormal
noises, and worn bearings or bushings indicate
Figure 6-22.Grid-type flexible coupling.
Wedges, or shims, are placed under the bases of
both the driven and driving units to facilitate alignment
when the machinery is installed. Jacking screws can
also be used to level the units. When the pump or
driving unit, or both, need to be shifted sideways to
align the couplings, side brackets are welded in
convenient spots on the foundations, and large
setscrews are used to shift the units sideways or
endwise. When the wedges or other packing have been
adjusted so the outside diameters and faces of the
coupling flanges run true as they are manually
revolved, the chocks should be fastened, the units
should be securely bolted to the foundation, and the
coupling flanges should be bolted together.
These ALIGNMENTS MUST BE CHECKED
from time to time and misalignments promptly
corrected. There are three devices in use for checking
the alignments-a 6-inch scale, a thickness gauge, and a
Shaft alignment should be checked whenever the
pump is opened up and whenever a noticeable
vibration is observed. When shafts are found out of
line or inclined at an angle to each other, the unit
should be aligned to avoid shaft breakages and renewal
of bearings, pump casing wearing rings, and throat
bushings. The appropriate technical manual should be
consulted when you are aligning the pump.
In a centrifugal pump installation fitted with an
internal water-lubricated bearing inside the pump
casing (such as condensate pumps), an adequate supply
of clean water must be supplied to the bearing for
lubricating and cooling. Several of the following types
of materials are used for internal water-lubricated